Starch consists of a mixture of amylose (15-30% w/w) and amylopectin (70-85% w/w). Amylose consists of linear chains of α-1,4-linked glucose units having a molecular weight (MW) from about 60,000 to about 800,000. Amylopectin is a branched polymer containing the same α-1,4-linked glucose units, as well as α-1,6 branch points every 24-30 glucose units; its MW may be as high as 100 million.
Sugars from starch, in the form of concentrated dextrose syrups, are currently produced by an enzyme catalyzed process involving: (1) liquefaction (or thinning) of solid starch with an α-amylase into dextrins having an average degree of polymerization of about 7-10, and (2) saccharification of the resulting liquefied starch, i.e., starch hydrolysate, with amyloglucosidase (also called glucoamylase). The resulting syrup has a high glucose content. Much of the glucose syrup that is commercially produced is subsequently enzymatically isomerized to a dextrose/fructose mixture known as isosyrup.
α-Amylases (EC 3.2.1.1) hydrolyze starch, glycogen, and related polysaccharides by cleaving internal α-1,4-glucosidic bonds at random. These enzymes have a number of important commercial applications, including starch liquefaction, textile desizing, starch modification in the paper and pulp industry, grain processing, backing and brewing. α-Amylases also can be used in automatic dishwashing detergent and laundry detergent formulations, including those containing bleach, to remove starchy stains during washing. The α-amylase from Bacillus sp. no. 707 shows particularly advantageous performance when used in these applications. Unfortunately, this α-amylase is not expressed at high levels, complicating its economical manufacture and commercial use.
α-Amylases are isolated from a wide variety of bacterial, fungal, plant and animal sources. Many industrially important α-amylases are isolated from Bacillus sp., in part because of the generally high capacity of Bacillus to secrete amylases into the growth medium. Bacillus sp. A 7-7 (DSM 12368), for instance, secretes α-amylase at advantageously high levels. Although the Bacillus sp. A 7-7 α-amylase can be produced economically, the enzyme does not perform as well as the α-amylase from Bacillus sp. no. 707. Accordingly, there is a need in the art to express the better performing variant of Bacillus sp. no. 707 α-amylase at production levels comparable to, for example, the Bacillus sp. A 7-7 α-amylase. Such a variant would be useful in more effective and economical detergent formulations or other formulations.